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A few publications are surveyed in this section, and relevant data of the selected papers are shown in Table 1, which show that many alternative amendments/techniques exist for the reclamation of sodic soils, though gypsum is still the dominant reclamation material. Doses of amendments and speed of reclamation vary widely depending on experimental conditions—most importantly the sodicity level. Some biological methods of reclamation have recently gained popularity. Jesus et al. (2015) suggested to combine phytoremediation with reclamation, which is an old approach. Kumar et al. (2021) reported that Prosopis legume trees improve soil conditions in the following salinity reduction order: P. juliflora (64.5%) > P. chilensis (61.5%) > P. articulata (59.8%); and the increase of carbon stock showed the following order: P. alba > P. juliflora > others. Abate et al. (2021) reported that grass planting combined with gypsuming improved soil properties, and Cynodon dactylon and Chloris gayana have an ameliorative effect on infiltration and soil salinity/sodicity/alkalinity that is comparable to small gypsum doses.
Table 1. Main features of some recent studies on the application of amendments/techniques used to reclaim sodic soils
Soil salinity/sodicity and textural class; Experimental conditions; Presence of crops Amendment Starting (s)/Control (c) and final (f) soil ESP/SAR Doses of amendments/(t/ha) Duration of experiment Comments Country Reference Saline-sodic irrigated small field plots Siltloam soil with Cynodon dactylon/C. gayana G ESPs 57 ESPf 9 2.5 131 d Effect of grasses X gypsum on infiltration was the main topic Ethiopia Abate et al., 2021 Saline-sodic soil in pot experiment G ESPc 21 ESPf 2.1 47.7 112 d Effect on quinoa performance was the main topic
Chile Alcívar et al., 2018 with two C. quinoa varieties, Siltloam Humic substances ESPc 21 ESPf 3.7 5 112 d Endosalic Sodic Regosols Biochar ESPc 21 ESPf 4.5 22 112 d Nonsaline sandy loam in lysimeter
with rice/wheat irrigated with saline/sodic waterG, sulfuric acid ESPc 5.5 ESPf w/o G 31 ESPf w/ G 18.4 Control=irrigated with nonsaline/nonsodic water For neutralizing RSC 20 yr Soil structure and water movement were the main topics India Minhas et al., 2021 Flue gas desulfurization gypsum
Field experiment on various soilsG 60% improvement 0.3 to 60 Various 59 sites were studied China Wang et al., 2021a Saline-sodic soil in field experiment
Clay soil with alfalfaG ESPc36 ESPf 8 180 yearly 4 yr Flue gas desulfurization gypsum China Ying et al., 2021 Saline-sodic soil in field experiment
Silt soil with wild halophyte plantsG ESPs 42 ESPf 15 10.9 25 w Leaching was the main focus Jordan Batarseh, 2017 Saline-sodic soil in field experiment
Sandy clay loam soil with rice/wheatG SARc 280 SARf 20 11 2 yr Leaching experiment Pakistan Murtaza et al., 2009 Sodic loam soil in field experiment
Leptic Natrudolls on hayfieldG SARs 5.39 SARf 1.5 9.1 4 m Microbiological indication of reclamation in drainage experiment was the main focus US Dose et al., 2015 Saline-sodic soil in pot experiment
Barley was grownVoltage was generated Soluble sodium decreased by 82% None 61 d Plant microbial desalination cell was tested China Han et al., 2021 Saline-sodic soil extract in test-tube
Salt tolerant Bacillus subtilis cultureBacterium fermentation product Soluble Na decreased by 28% None 4 h Ca-P compound precipitation was inhibited China Wang et al., 2021b Saline-sodic soil in field experiment
Clay soil with wheatG ESPc 19 ESPf 20 17 2 yr Tillage was also tested Egypt Ding et al., 2021 Sulfuric acid ESPc 19 ESPf 14 4.3 2 yr Vermicompost ESPc 19 ESPf 15 10 2 yr Saline-sodic soil in pot experiment
Clay loam soil with oatVinegar residue +S-K fertilizer ESPc 75 ESPf 45 1.3 2 m Nonsodic saline soil was also tested China Fan et al., 2018 Notes: G, gypsum; RSC, Residual Sodium Carbonate; ESP, exchangeable sodiumpercentage; SAR, Sodium Adsorption Ratio; h, hour; d, day; w, week; m, month; yr, year Among chemical methods for reclamation, gypsuming and the application of organic matter remain the most popular. Alcívar et al. (2018) studied the effect of these amendments and found that the combination of biochar, humic substances, and gypsum had superior effect on soil and both quinoa genotypes. Minhas et al. (2021) evaluated a 20-year-old reclamation experiment in which soils were irrigated with alkali water and found that watering with high-Residual Sodium Carbonate water decreased soil water storage capacity compared to good-quality water, whereas gypsum and sulfuric acid increased soil water storage capacity; nevertheless, the effect on post-infiltration water storage did not reach below the depth of 30 cm. Wang et al. (2021a) reported the reclamation of sodic soils with flue gas desulfurization gypsum (FGDG). A meta-analysis of 59 locations showed that FGDG had several positive effects on soil and plants, although heavy metal concentration increased in the soil. Ying et al. (2021) described the effect of flue gas desulfurization steel slag on sodic soil properties, where 180 t/ha was applied in each of three consecutive years. Increasing duration improved the reclamation effect, and the effect on physical and chemical soil properties was rapid, but the treatment resulted in salt accumulation at a greater soil depth.
Leaching studies continue to be widespread. Callaghan et al. (2017) reported that although approximately 30% of salts could be leached during the first year of the experiment, water-table rise limited leaching in the second year in clay soil. Batarseh (2017) studied the leaching of calcareous saline-sodic soils in Jordan. All three treatments—gypsum, fresh water (1 dS/m), and saline water (8 dS/m)—reduced salinity, but application of gypsum hastened leaching to twice the original velocity. Murtaza et al. (2009) studied the effects of combinations of irrigation water quality, amendment, and crop rotation on soil properties and economic benefits in saline-sodic soil. According to the results, gypsum/manure and 1st saline-sodic water + 2nd fresh water irrigation provided optimal yield/economic benefit in rice/wheat rotation. On the other hand, soil physical properties were best improved with gypsum, but chemical properties with manure. In order to account for the dispersing effect of rainwater, according to Suarez (2013), more gypsum must be applied regularly when irrigating with saline/sodic water in California. Shafiefar et al. (2021) used HYDRUS-1D for leaching estimation. An inverse method was used to estimate the desalination curve, which was compared to measured data. The results showed that leaching with or without sulfuric acid did not show significant differences in a calcareous gypsiferous saline-sodic soil; moreover, earlier and shallower changes were better estimated than later and deeper ones. Zhurba et al. (2019) suggested specific practical steps for reclaiming/leaching saline-sodic soils in rice cultivation, including technical guidelines for applying sulfuric acid depending on lime/gypsum/soil organic matter/texture/pH conditions in the soil. As a contrast, not amendments, but loosening provided best leaching effect in the study of Shaygan et al. (2018).
Organic matter has long been used as an amendment and is still widely applied today. Ding et al. (2021) combined tillage with vermicompost on an irrigated saline-sodic wheat field in Egypt over two years. They found that the vermicompost had a better effect than gypsum or sulfuric acid, and deep tillage improved the effect of amendments on soil properties and yield. Elkhlifi et al. (2021) used phosphate-lanthanum coated sewage sludge biochar in ryegrass cultivation and found that it provided a large amount of phosphorus and decreased the CaCO3 content due to a decomposition reaction. Fan et al. (2018) reported the effect of vinegar residue combined with Si-K fertilizer on saline and saline-sodic soil. They found that vinegar residue reduced the sodicity of saline and saline-sodic soils. Increasing the dose of Si-K fertilizer further decreased sodicity but increased EC and pH.
The reclamation of sodic soils with microbial products is a very recent development. Han et al. (2021) developed a plant microbial desalination cell and also a soil microbial desalination cell based on the processes of ion migration, plant absorption, bioremediation, and microbial activity. They showed that the plant microbial desalination cell produced a larger effect than the soil microbial desalination cell. Li et al. (2019) published a review on the effect of Cyanobacteria for reclaiming salt-affected soils and stated that, in pot cultures, positive effects were found in the few studies so far. Wang et al. (2021b) studied Bacillus subtilis broth and found that it provided active phosphate for plants; furthermore, the fermentation liquid suppressed phosphate crystallization and also reduced the pH value, but it increased EC. Dose et al. (2015) studied the functional gene and enzyme activity indicators of sodic soil reclamation by using successional vector trajectories. They found that number of ammonia-oxidizing bacterial gene copies was higher where cropland was amended with gypsum, and that indicators were sensitive to cropping and amendments but not to drainage installation. Xu et al. (2021) studied the composition of bacterial communities in salinity/sodicity gradients in a study carried out at Da’an station (Jilin Province, China) and found large differences between topsoil and 80–100 cm depth layers. Both salinity and sodicity were strong factors determining the bacterial composition.
There are other miscellaneous techniques used in the reclamation of saline and sodic soils, such as the use of Fe4[Fe(CN)6]3 for fixing NaCl. In one study, when iron (III) ferrocyanide, a crystallization inhibitor, was added to saline soils, 29%–57% of NaCl was removed after 7 d (Daigh et al., 2016). In another study, after two weeks of iron (III) ferrocyanide application, the amount of salt crystals deposited on the soil surface increased with increasing application rate (Angin et al., 2019).
During their study of the effect of frost, Li et al. (2021a) found that frost heaving improved soil structure in the Yellow River Delta. Rather than particle size distribution, dense arrangement caused unfavorable soil physical properties. They found that the freezing of moister (10%–25% moisture) soil improved structure more. Al-Busaidi et al. (2013) used anionic polyacrylamide and/or gypsum for protecting sodic soils from erosion successfully.
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Abstract: For centuries, reclamation of sodic soils has been an essential part of cropping practices in several parts of the world. Parallel to increasing population, the need for new cropland constantly re-evaluates land suitability concepts. Therefore, the importance of sodic soils as potential croplands is increasing worldwide. Although theoretically farmers can choose from a wide variety of reclamation options, according to profitability, business plans, and human and financial resources, in practice, few reclamation methods are applied at large scale. This article touches on the early history, 20th Century intensive research, and current trends of sodic soil reclamation. New approaches such as leaching, chemical amendments, addition of organic material, and biological and microbial improvements are discussed, and also brand-new approaches are reviewed. The early history is reviewed using historical books, the achievements of the last hundred years using basic technical literature, mostly books, and the current approaches of our time with fresh publications, mostly papers and two very recent conferences published in English.
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Key words:
- gypsuming /
- liming /
- chemical reclamation /
- new technology /
- sodic soil
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Table 1. Main features of some recent studies on the application of amendments/techniques used to reclaim sodic soils
Soil salinity/sodicity and textural class; Experimental conditions; Presence of crops Amendment Starting (s)/Control (c) and final (f) soil ESP/SAR Doses of amendments/(t/ha) Duration of experiment Comments Country Reference Saline-sodic irrigated small field plots Siltloam soil with Cynodon dactylon/C. gayana G ESPs 57 ESPf 9 2.5 131 d Effect of grasses X gypsum on infiltration was the main topic Ethiopia Abate et al., 2021 Saline-sodic soil in pot experiment G ESPc 21 ESPf 2.1 47.7 112 d Effect on quinoa performance was the main topic
Chile Alcívar et al., 2018 with two C. quinoa varieties, Siltloam Humic substances ESPc 21 ESPf 3.7 5 112 d Endosalic Sodic Regosols Biochar ESPc 21 ESPf 4.5 22 112 d Nonsaline sandy loam in lysimeter
with rice/wheat irrigated with saline/sodic waterG, sulfuric acid ESPc 5.5 ESPf w/o G 31 ESPf w/ G 18.4 Control=irrigated with nonsaline/nonsodic water For neutralizing RSC 20 yr Soil structure and water movement were the main topics India Minhas et al., 2021 Flue gas desulfurization gypsum
Field experiment on various soilsG 60% improvement 0.3 to 60 Various 59 sites were studied China Wang et al., 2021a Saline-sodic soil in field experiment
Clay soil with alfalfaG ESPc36 ESPf 8 180 yearly 4 yr Flue gas desulfurization gypsum China Ying et al., 2021 Saline-sodic soil in field experiment
Silt soil with wild halophyte plantsG ESPs 42 ESPf 15 10.9 25 w Leaching was the main focus Jordan Batarseh, 2017 Saline-sodic soil in field experiment
Sandy clay loam soil with rice/wheatG SARc 280 SARf 20 11 2 yr Leaching experiment Pakistan Murtaza et al., 2009 Sodic loam soil in field experiment
Leptic Natrudolls on hayfieldG SARs 5.39 SARf 1.5 9.1 4 m Microbiological indication of reclamation in drainage experiment was the main focus US Dose et al., 2015 Saline-sodic soil in pot experiment
Barley was grownVoltage was generated Soluble sodium decreased by 82% None 61 d Plant microbial desalination cell was tested China Han et al., 2021 Saline-sodic soil extract in test-tube
Salt tolerant Bacillus subtilis cultureBacterium fermentation product Soluble Na decreased by 28% None 4 h Ca-P compound precipitation was inhibited China Wang et al., 2021b Saline-sodic soil in field experiment
Clay soil with wheatG ESPc 19 ESPf 20 17 2 yr Tillage was also tested Egypt Ding et al., 2021 Sulfuric acid ESPc 19 ESPf 14 4.3 2 yr Vermicompost ESPc 19 ESPf 15 10 2 yr Saline-sodic soil in pot experiment
Clay loam soil with oatVinegar residue +S-K fertilizer ESPc 75 ESPf 45 1.3 2 m Nonsodic saline soil was also tested China Fan et al., 2018 Notes: G, gypsum; RSC, Residual Sodium Carbonate; ESP, exchangeable sodiumpercentage; SAR, Sodium Adsorption Ratio; h, hour; d, day; w, week; m, month; yr, year -
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